| United States Numbered Highway System | |
|---|---|
 Types of special routes in the U.S. | |
| Highway names | |
| US Highways | U.S. Highway nn (US nn) U.S. Route nn (US nn) |
| Special routes |
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| System links | |
A special route of the United States Numbered Highway System is a route that branches off a U.S. Highway in order to divert traffic from the main highway. Special routes are distinguished from main routes by, in most cases, the addition of an auxiliary plate that describes what type of route it is, while the main highway carries no such sign. In some locations, a single letter is placed after the route number to denote the special route type in lieu of the auxiliary plate. Among members of the roadgeek community, these routes are often called auxiliary or bannered U.S. Highways.
There are four main types of special routes — alternate, business, bypass, and temporary; though other route types exist.
- Alternate routes exist where an additional road is needed to meet traffic demands. They are to be of equal character and quality compared to the main road.
- Business routes carry traffic through the central business district of a community while the main highway goes around the community.
- Bypasses serve the opposite purpose of business routes. Truck routes are a subset of bypasses.
- Temporary routes complete a gap between two segments of main highway that exists because the main highway has not been fully constructed.
A unique type of route in the U.S. Route system uses directional letter suffixes following the route number. These are known as divided U.S. Routes and are generally not considered to be special routes.
The following U.S. Highway special routes have existed:
- Routes are sorted by position along the main route, from south to north and west to east.
- Defunct routes are listed in italics.
